It is known to fabricate the valves of electromechanical actuated fuel injectors from materials, such as stainless steels, by metalworking processes, such as milling and grinding. While such processes can produce high degrees of accuracy in finished parts, they possess certain inherent limitations. Specifications for tolerable leakage are becoming increasingly strict, pushing such processes to their limits.
Fuel injectors having valves made from silicon elements, have been suggested to provide even closer tolerances in finished parts; for example, see U.S. Pat. Nos. 4,628,576; 4,647,013; 4,756,508; 4,826,131; 4,808,260 and 4,907,748.
The present invention relates to improvements in such silicon valves.
One aspect of the invention relates to an organization and arrangement of a composite silicon valve that provides for precise control of valve lift while also disposing the gate directly in the flow path through the valve so that when the injector is flowing, the gate remains in the flow path, rather than to one side of the flow path, and this is especially important for a single stream fuel injector that injects fuel coaxial with the fuel injector's main longitudinal axis.
Another aspect of the invention relates to improved compliancy of the gate to the seat when the valve is closed. This is achieved by making one or both of the silicon sealing surfaces of the gate and/or seat of P+ silicon preferably as a surface layer having a preferred thickness in the range of about 10 microns to about 30 microns.
Still another aspect of the invention relates to the inclusion of a thin disc orifice member formed from silicon which comprises one or more metering orifices for metering the flow from the valve.